1. Field of the Invention
The present invention relates to a charged particle beam exposure method and a charged particle beam exposure apparatus, and more particularly, to a method for creating exposure data for exposing patterns on a semiconductor wafer by means of a charged particle beam, such as an electron beam, and a charged particle beam exposure apparatus for implementing this method.
2. Description of the Related Art
The exposure of a charged particle beam, such as an electron beam, is able to expose patterns of the sub-micron order and is used in the fabrication of highly integrated LSIs. In particular, recently, in addition to its use in forming masks, methods whereby the charged particle beam is irradiated and exposed directly onto the resist formed on a semiconductor wafer have been used.
In the design stage for LSIs, pattern data for a multi-layered structure is created in order to form a desired integrated circuit. The resist on a semiconductor wafer or the resist on a mask substrate is exposed in accordance with this pattern data. A charged particle beam is irradiated onto the resist layer, and the energy of the beams causes the resist to undergo a chemical reaction.
In this case, it is important to take note of the proximity exposure effect, which is caused by forward or backward scattering of the beam in the resist when the charged particle beam is irradiated onto the resist. The proximity exposure effect is a phenomenon whereby the energy of a charged particle beam irradiated onto a particular region is caused to spread into adjacent regions due to scattering of the beam. For example, in a region where the exposure pattern density is high, after developing, a pattern may have broadened due to the effect of beam energy from a charged particle beam irradiated onto an adjacent exposure pattern region. Alternatively, in a region where the exposure pattern density is low, there will be no effect due to energy from adjacent regions, and hence the pattern after developing will be condensed or narrow. A further alternative is that Coulomb interaction, which is a type of forward scattering, will give rise to blurring of the beam, in turn leading to a decline in pattern accuracy.
Therefore, it is necessary to correct the designed exposure data, by taking this proximity exposure effect into consideration. The present applicants have proposed such a method for correcting exposure data in Japanese Patent Application H9-269081, dated Oct. 1, 1997 (laid-open number H11-111595, dated Apr. 23, 1999), or U.S. Pat. No. 6,087,052, dated Jul. 11, 2000.
Briefly stated, in the methods proposed in these patent applications, a plurality of correction areas are generated in a sub-field, the pattern density in each of these correction areas is corrected in accordance with the effects due to the pattern densities in surrounding correction areas so that an corrected pattern density is determined which takes the proximity exposure effect into account, the main quantity of exposure (exposure intensity) for the pattern containing the correction areas is corrected, and furthermore, supplementary exposure patterns are generated for correction areas where the quantity of exposure is insufficient.
According to this method, the main quantity of exposure applied to each pattern is provisionally corrected by taking account of the proximity exposure effect from exposure of adjacent areas, and then supplementary exposure is performed with respect to regions within the pattern where the pattern density is low and which have not been provided with sufficient exposure energy to convert the resist. By adjusting the main quantity of exposure, broadening of the pattern due to excessive quantity of exposure is prevented, and furthermore, by performing supplementary exposure, narrowing of the end sections of the pattern, and the like, due to insufficient quantity of exposure, can be prevented.
However, a first problem lies in the fact that additional generation of supplementary exposure patterns requires new beam shot operations, thereby increasing the total number of beam shots required to fabricate an LSI, and hence causing a decline in throughput.
A second problem relates to the fact that the supplementary exposure patterns are exposure patterns having a relatively low quantity of exposure, which are appended in cases where the main quantity of exposure for the pattern is insufficient. Therefore, in many cases, these supplementary exposure patterns are required at the periphery or end sections of a pattern, where the proximity exposure effect from adjacent areas is small.
When exposing supplementary exposure patterns having a low quantity of exposure of this kind at the corner sections of a pattern, or at the end sections of a long and narrow pattern, regions receiving low exposure energy spread at these corner sections and end sections, and hence cause a decline in the contrast of the developed pattern at the corner sections and end sections, after exposure. In other words, the cross-section of the developed pattern tends to form a hem shape at the corner sections and end sections, and in plan view, it tends to have a rounded shape. Therefore, it has been sought to reduce as far as possible the generation of supplementary exposure patterns at the corner sections and end sections of a pattern.
A third problem is that the electrons in the irradiated beam are subject to a degree of spreading, due to Coulomb interaction of the electrons, when the charged particle beam is irradiated. More specifically, blurring of the irradiation beam occurs. This blurring of the beam is of significant magnitude in pattern design rules involving magnitudes of no more than 0.1 xcexcm, in particular. Therefore, it has become necessary to perform pattern correction in a suitable manner which takes account of blurring of the beam.
Therefore, it is an object of the present invention to provide a charged particle beam exposure method and apparatus, whereby the number of supplementary exposure patterns can be reduced as far as possible.
It is a further object of the present invention to provide a charged particle beam exposure method and apparatus, whereby generation of supplementary exposure patterns at the end sections of long and narrow patterns can be restricted as far as possible.
It is yet a further object of the present invention to provide a charged particle beam exposure method and apparatus, whereby decline in exposure pattern accuracy due to blurring of the beam can be prevented.
In order to achieve the aforementioned objects, a first aspect of the present invention is a charged particle beam exposure method, wherein exposure data having exposure pattern data is generated from pattern data having a plurality of patterns, and a material is exposed in accordance with the exposure data; comprising the steps of: (a) generating a plurality of correction areas with respect to the patterns; (b) dividing a pattern of the pattern data which is long and narrow and has a height to width ratio greater than a reference value, into a plurality of patterns; (c) determining a pattern area density within the correction areas, and revising the pattern density of the correction area in accordance with the pattern densities of correction areas surrounding said correction area and the distance between the respective correction areas; (d) determining a main quantity of exposure for each divided pattern in accordance with the highest corrected pattern density of the corrected pattern densities of the correction areas intersecting with the divided pattern; (e) generating supplementary exposure patterns in the correction areas within the divided patterns where there is a shortage of exposure energy in the case of the main quantity of exposure; and (f) exposing the material, in accordance with exposure pattern data comprising the supplementary exposure patterns added to the pattern data.
According to this first aspect of the present invention, long and narrow patterns are divided into a plurality of patterns, and the optimum main quantities of exposure are determined for each of these divided patterns. In regions where there is a shortage of exposure energy with this main quantity of exposure, a supplementary exposure pattern is generated and the exposure shortage is resolved. Since an optimum main quantity of exposure is determined for each divided pattern, it is possible to reduce the number of supplementary exposure patterns required.
Furthermore, in order to achieve the aforementioned objects, a second aspect of the present invention is a charged particle beam exposure method, wherein exposure data having exposure pattern data is generated from pattern data having a plurality of patterns, and a material is exposed in accordance with the exposure data; comprising the steps of: (a) determining blurring of the beam due to spreading of the beam according to the maximum size of the exposure beam size used to draw the pattern, and amending the pattern to be reduced in accordance with the blurring of the beam; and (b) exposing the material in accordance with exposure pattern data determined in accordance with the amended pattern.
According to this second aspect of the present invention, the blurring of the beam due to Coulomb interaction is determined in accordance with the beam size used to draw the patterns, and the patterns are amended to be reduced in size according to this blurring of the beam. Therefore, the pattern accuracy after exposure and development is improved.
In order to achieve the aforementioned objects, a third aspect of the present invention is a charged particle beam exposure method whereby exposure data having exposure pattern data is generated from pattern data having a plurality of patterns, and a material is exposed in accordance with the exposure data; comprising the steps of: (a) generating a plurality of correction areas with respect to the patterns; (b) determining a pattern area density within the correction areas, and revising the pattern area density of said correction area in accordance with the pattern area densities of correction areas surrounding said correction area and the distance between the respective correction areas; (c) determining a main quantity of exposure for each pattern in accordance with the highest corrected pattern area density of the corrected pattern area densities of the correction areas intersecting with the boundaries of the pattern; (d) generating supplementary exposure patterns in the correction areas within the patterns where there is a shortage of exposure energy in the case of the main quantity of exposure; and (e) exposing the material, in accordance with exposure pattern data having the supplementary exposure patterns added to the pattern data.
According to this third aspect of the present invention, the main quantity of exposure for the patterns is corrected with reference to the highest corrected pattern area density in the correction areas intersecting with the pattern boundaries. This highest corrected pattern density is generally called the pattern area density and is the representative area density of the pattern. According to this method, it is possible to set the main quantity of exposure for the pattern to the optimum quantity of exposure for the pattern boundaries. Therefore, the number of supplementary exposure patterns generated at the pattern boundaries can be reduced.
In order to achieve the aforementioned objects, a fourth aspect of the present invention is a charged particle beam exposure method for exposing a material by means of a charged particle beam transmitted through a block mask having a plurality of patterns, comprising the steps of: (a) generating a plurality of correction areas with respect to patterns of the block mask; (b) determining a pattern area density within the correction areas, and revising the pattern density of said correction area in accordance with the pattern densities of correction areas surrounding said correction area and the distance between the respective correction areas; (c) determining quantities of exposure for each pattern in accordance with the highest corrected pattern density of the corrected pattern densities of the correction areas intersecting with the boundaries of the patterns, and setting the smallest quantity of exposure among the quantities of exposure for the plurality of patterns within the block mask as the main quantity of exposure for the block mask; (d) generating supplementary exposure patterns in the correction areas within the patterns where there is a shortage of exposure energy in the case of the main quantity of exposure; and (e) exposing the material in accordance with the main quantities of exposure by means of a charged particle beam passing through the block mask, and further exposing the material according to the supplementary exposure patterns.
According to this fourth aspect of the present invention, it is possible to optimize the quantity of exposure for a block mask.